From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@linaro.org>
Subject: Re: [RFC 12/19] xen/passthrough:
 iommu_deassign_device_dt: By default reassign device to nobody
Date: Thu, 03 Jul 2014 13:07:41 +0100
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To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: xen-devel@lists.xenproject.org, stefano.stabellini@citrix.com, tim@xen.org
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Hi Ian,

On 07/03/2014 12:48 PM, Ian Campbell wrote:
> On Mon, 2014-06-16 at 17:17 +0100, Julien Grall wrote:
>> Currently, when the device is deassigned from a domain, we directly reassign
>> to DOM0.
>>
>> As the device may not have been correctly reset, this may lead to corrupt or
>> expose some part of DOM0 memory.
> 
> "corruption".
> 
> I'd go further and say "and we may have no way to reset some platform
> devices".

Ok.

>> If Xen reassigns the device to "nobody", it may receive some global/context
>> fault because the transaction has failed (indeed the context has been
>> marked invalid).
> 
> Can you describe here what happen in this case (I presume Xen tears down
> the iommu to quiesce them somehow?)

The SMMU drivers will mark the different Context Bank, S2CR, SMR as
invalid. If the device is attempt to access the memory then, we will
receive an interrupt in Xen.

Actually it's only happen once, if the device is still enabled when the
domain is shutdown.

Regards,

-- 
Julien Grall